Encrypted IM Tool Vulnerable To Eavesdropping

Bugs in instant messaging encryption tool Cryptocat left users' group chats vulnerable to eavesdropping for over a year, says security researcher.

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Cryptocat, a free tool designed to encrypt online chats, has been updated to fix errors that would have allowed an attacker to eavesdrop on chats. The vulnerability resulted from developers using below-minimum public key sizes or iterations. As a result, anyone who used a vulnerable version of Cryptocat to hold a group conversation, or who communicated with anyone using the software, could have had their communications easily intercepted.

That warning was sounded by security researcher Steve Thomas, who detailed the errors in a blog post. "If you used group chat in Cryptocat from Oct. 17th, 2011 to June 15th, 2013, assume your messages were compromised," he said. "Also if you or the person you are talking to has a version from that time span, then assume your messages are being compromised."

Thomas built a tool he calls DecryptoCat, which "cracks the ECC public keys generated by Cryptocat versions 1.1.147 through 2.0.41" in about a day, he said. Using the information generated by the tool, it would then take just a few minutes to crack any vulnerable Cryptocat key. Based on the coding errors he found, Thomas had harsh words for the chat tool's developers, who he labeled as being "incompetent." "I feel bad about calling them incompetent, but it is true. If you mess up in all the places I cared to check ... that's incompetence," he said.

In response, Cryptocat issued an apology, and said that the bug detailed by Thomas -- which they claimed left users' communications vulnerable for only seven months -- was rapidly fixed. "The vulnerability was quickly resolved and an update was pushed," said the Cryptocat development blog post. "We sincerely thank Steve for his invaluable effort."

The developers emphasized that it's impossible to keep software entirely free from bugs. "Bad bugs happen all the time in all projects," they said. "Cryptocat is not any different from any of the other notable privacy, encryption and security projects, in which vulnerabilities get pointed out on a regular basis and are fixed. Bugs will continue to happen in Cryptocat, and they will continue to happen in other projects as well. This is how open source security works."

Published: 2015-03-31The build_index_from_tree function in index.py in Dulwich before 0.9.9 allows remote attackers to execute arbitrary code via a commit with a directory path starting with .git/, which is not properly handled when checking out a working tree.